Abstract
Abstract. Growth of coastal dunes requires a marine supply of sediment. Processes that control the sediment transfer between the subtidal and the supratidal zone are not fully understood, especially in sand flats close to inlets. It is hypothesised that storm surge events induce sediment deposition on sand flats, providing fresh material for aeolian transport and dune growth. The objective of this study is to identify which processes cause deposition on the sand flat during storm surge conditions and discuss the relationship between the supratidal deposition and sediment supply to the dunes. We use the island of Texel (NL) as a case study, of which multiannual topographic and hydrographic datasets are available. Additionally, we use the numerical model XBeach to simulate the most frequent storm surge events for the area. Results show that supratidal shore-parallel deposition of sand occurs in both the numerical model and the topographic data. The amount of sand deposited is directly proportional to surge level and can account for more than a quarter of the volume deposited at the dunes yearly. Furthermore, storm surges are also capable of remobilising the top layer of sediment of the sand flat, making fresh sediment available for aeolian transport. Therefore, in a sand flat setting, storm surges have the potential of reworking significant amounts of sand for aeolian transport in periods after the storm and as such can also play a constructive role in coastal dune development.
Highlights
Coastal dunes are important natural flood defence features
Our present research suggests that, for a sand flat setting, a supratidal shore-parallel depositional ridge can form during a storm surge flooding, inducing the deposition of a certain amount of sand that is of the same order of magnitude as the amount of dune volume increase
Results suggest that supratidal deposition of sand is directly proportional to storm surge levels and wave energy
Summary
Coastal dunes are important natural flood defence features. They grow at the interface between land and sea by the interaction of biological processes, physical processes and geological conditioners (Hesp, 1983, 2002; Hesp and Walker, 2013; Sherman and Bauer, 1993; Bauer and Davidson-Arnott, 2002; Delgado-Fernandez and DavidsonArnott, 2011; van Puijenbroek et al, 2017). Aagaard et al (2004) linked the occurrence of onshore bar migration and its subsequent welding to the coast with sediment supply towards the dunes. Wave-driven currents, oscillatory components of the incident wave motions and effects of infra-gravity waves on currents are responsible for transporting sediment onshore, leading to a continuous supply of sediment from the subtidal (i.e. zone that stays below sea level) to the intertidal zone and, subaerial zone (i.e. known as supratidal zone, refers to the zone above the high tide level) (Aagaard, 2014). Aagaard et al (2004) linked the occurrence of onshore bar migration and its subsequent welding to the coast with sediment supply towards the dunes. Anthony et al (2006) showed that, for a tide-dominated beach on the coast of France, annual dune accretion depends on bar welding phenomena related to storm processes, which could account for 48 % of the overall dune change. Anthony (2013) showed that for the southern North Sea coastal system
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